1) Field of the Invention
The invention relates to the fluid conduits which form the outer retaining wall for an annular particulate bed used in a radial flow system mounted in a cylindrical vessel. In such systems a fluid typically is directed radially inwardly or outwardly into or out of the particulate bed through openings in the inner surfaces of a plurality of outer, vertically arranged conduit members or through openings in a cylindrical screen basket member which has a smaller diameter than the inner wall of the vessel. The fluid passes through openings in a vertically arranged center pipe which forms the inner retaining wall for the annular particulate bed.
2) Description of the Related Art
The vessel typically is a reactor which contains a bed of particulate material such as catalyst, absorbent, resins or activated carbon. The fluid which passes through the particulate bed in a radial direction is usually a gas but it could also be a liquid or a liquid/gas mixture. In prior art systems the outer wall support for the annular particulate bed is often a ring of individual scallops members which have convex inner surfaces and outer surfaces which conform to the wall of the vessel. The scallops members can be formed from metal plates which contain perforations smaller in diameter than the size of the particulate material. They can also be formed with their convex inner surface comprising a screen element having a plurality of closely spaced wires welded to support rods. Such scallops are often sized so they can be installed or replaced when required by lifting them through an opening in the top of the vessel. Although the convex surface of the scallops which supports the particulate bed is quite strong, the convex shape causes the thickness of the annular bed to be non-uniform. Thus, the flow distribution through the bed is non-uniform and more flow will take place at the location on the scallops where their convex surface is closest to the center pipe and the pressure drop is lowest. Since the bed must usually have a predetermined minimum thickness, the convex scallops shape means that additional particulate material must be provided to fill all of the space which is radially outwardly of a circle containing the radially innermost portion of the scallops. Where the particulate material is one which contains a precious metal such as platinum, the need for additional material can be very expensive. In addition, the tendency for flow to take place where the flow distance is at its shortest results in uneven contact between the fluid to be reacted and the particulate material in the bed. This uneven flow can result in the need to replace the particulate material sooner than if the flow was entirely uniform.
Another type of prior art system includes a cylindrical screen basket member which is spaced inwardly from the outer wall of the vessel. Such a cylindrically shaped screen basket member cooperates with an inner screen pipe member to cause the particulate bed positioned between such inner and outer members to have a uniform thickness. However, the systems is quite expensive since the large diameter screen cannot be installed or removed through a small upper opening in the vessel, as can the scallops type screen.
Examples of prior art systems which have scallops members around the inside surface of the outer vessel wall include Hansen, Jr. U.S. Pat. No. 3,167,399 and Koves et al U.S. Pat. No. 5,209,908. Farnham U.S. Pat. No. 4,374,094 shows vertical screen segments surrounding an annular catalyst bed which are spaced from the side wall of the vessel. Schuurman U.S. Pat. No. 4,540,547 shows a moving bed reactor wherein a ring of screen segments surrounds a centrally located catalyst bed and separates the catalyst from the outer annular chamber which receives the effluent after it passes through the screen surfaces. Nagaoka E. P. Publication 0 483 975 A1 shows a device for holding particulate catalyst in a radial flow reactor which comprises a ring of vertically arranged containers having abutting side walls and screened inner walls, the containers being filled with catalyst and positioned between an annular outer fluid chamber and an inner cylindrical fluid chamber.